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## Modulasi Sudut (2)

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**Modulasi Sudut (2)**Levy Olivia MT**3.3.3 Implementation of Angle Modulators and Demodulators**• Design an oscillator whose frequency changes with the input voltage. • Voltage-controlled oscillator • Varactor diode - capacitance changed with the applied voltage. • A inductor with the varactor diode is used in the oscillator circuit.**Let the capacitance of the varactor diode is given by**• When m(t) = 0, the frequency of the tuned circuit is given by • In general for nonzero m(t), we have • Assuming that • We have**Indirect method for generation of FM and PM signals**• generate a narrow band angle-modulated signal • change the narrow band signal to wideband signal**Generate wideband angle-modulated signals from narrow band**angle-modulated signals • frequency multiplier • implemented by nonlinear device and bandpass filters • Using down converter**A nonlinear device followed by a bandpass filter tuned to**the desired center frequency can be used as frequency multiplier. • For example, assume a nonlinear device has the function • The output signal will be • The frequency is multiplied by a factor of 2.**FM demodulation**• generate an AM signal • use AM demodulator to recover the message signal • Pass the FM signal through a filter with response • If the input to the system is • the output • The above signal is an AM signal.**FM to AM converter: Tuned circuit implementation**But, usually the linear region of the frequency characteristic may not be wide enough.**Balanced discriminator**• use two tuned circuits • connect in series to form a linear frequency response region.**FM demodulator with phase-locked loop (PLL)**• Input : • VCO output: • Phase Comparator:**By taking the Fourier transform**• Suppose that we design G(f) such that v(t) is the demodulated signal